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docs: We're not going to use backslashes for the with statement (#4564)

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Jelle Zijlstra 2025-01-28 18:29:05 -08:00 committed by GitHub
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docs/the_black_code_style/future_style.md
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@ -2,6 +2,8 @@
## Preview style
(labels/preview-style)=
Experimental, potentially disruptive style changes are gathered under the `--preview`
CLI flag. At the end of each year, these changes may be adopted into the default style,
as described in [The Black Code Style](index.md). Because the functionality is
@ -262,52 +264,3 @@ s = ( # Top comment
# Bottom comment
)
```
## Potential future changes
This section lists changes that we may want to make in the future, but that aren't
implemented yet.
### Using backslashes for with statements
[Backslashes are bad and should be never be used](labels/why-no-backslashes) however
there is one exception: `with` statements using multiple context managers. Before Python
3.9 Python's grammar does not allow organizing parentheses around the series of context
managers.
We don't want formatting like:
```py3
with make_context_manager1() as cm1, make_context_manager2() as cm2, make_context_manager3() as cm3, make_context_manager4() as cm4:
... # nothing to split on - line too long
```
So _Black_ will, when we implement this, format it like this:
```py3
with \
make_context_manager1() as cm1, \
make_context_manager2() as cm2, \
make_context_manager3() as cm3, \
make_context_manager4() as cm4 \
:
... # backslashes and an ugly stranded colon
```
Although when the target version is Python 3.9 or higher, _Black_ uses parentheses
instead in `--preview` mode (see below) since they're allowed in Python 3.9 and higher.
An alternative to consider if the backslashes in the above formatting are undesirable is
to use {external:py:obj}`contextlib.ExitStack` to combine context managers in the
following way:
```python
with contextlib.ExitStack() as exit_stack:
cm1 = exit_stack.enter_context(make_context_manager1())
cm2 = exit_stack.enter_context(make_context_manager2())
cm3 = exit_stack.enter_context(make_context_manager3())
cm4 = exit_stack.enter_context(make_context_manager4())
...
```
(labels/preview-style)=